How can I extend te MembershipUser class w/o multiple inheritance?

Question

At the top level I have a Person class. Next I want .NET's MembershipUser class to inherit from it, because a member is a person. However I want to extend the MembershipUser class which means, I think, I need to create my OWN MembershipUser class which inherits from MembershipUser and then adds my own properties. But once I do that, I can no longer inherit from Person due to multiple inheritance rules (ASP.NET 2.0).

Answer 1

You can solve this by creating an interface, IPerson and replacing your concrete Person class with a class which inherits from MembershipUser and implements IPerson.

You could also keep your concrete Person, create IPerson and have your own class encapsulate a Person instance and inherit from MembershipUser while implementing IPerson.

In either case, anywhere where you once used a concrete Person type you should replace with IPerson (such as method arguments).

interface IPerson
{
    string LastName { get; set; }
    // ...
}

class MyMembershipUser : MembershipUser, IPerson
{
    private Person _person = new Person();

    // constructors, etc.

    public string LastName
    {
     get { return _person.LastName; }
     set { _person.LastName = value; }
    }
}

Alternatively you could continue using Person and have it encapsulate a MembershipUser instance (as part of a constructor) and include an explicit cast for Person to MembershipUser when needed...

class Person
{
    private readonly MembershipUser _mu;
    public Person(MembershipUser mu)
    {
     _mu = mu;
    }

    public static explicit operator MembershipUser(Person p)
    {
     // todo null check
     return p._mu;
    }
}

// example
var person = new Person(Membership.GetUser("user"));
Membership.UpdateUser((MembershipUser)person);

I would go with the interface implementation solution myself.